The front wheel of a motorcycle is usually linked to the frame by a pair of fork tubes. These tubes house the front suspension and usually include springs and compartments filled with fork oil to act as a shock absorber, which protects the rider from bumps and vibrations as the vehicle travels uneven surfaces. The most common form of fork commercially available is a telescopic fork which uses fork tubes which contain the suspension components (coil springs and damper) internally. This design is simple and inexpensive to manufacture, and relatively light compared to designs based on external components and linkage systems.
The systems that rely on using fork oil as a damper often use a fork cartridge as a means of providing regressive damping. The self-contained cartridge in a cartridge style front fork system contains spring covered orifices regulating fork oil flow. The use of the self-contained cartridge allows the fork system to be stiffer when responding to small bumps and stiffer when responding to larger bumps. This cartridge in a cartridge style front forks needs to be removed from time to time for servicing and to replenish or replaced the oil used in the fork tube and cartridge. A common configuration used on motorcycles includes a fork cartridge which is filled with oil, and this fork cartridge is then fitted within the fork tube. The fork cartridge is screwed into the inner bore of a fork cap, and then this fork cap is screwed into the bore of a fork tube. In order to remove or replace the oil, it is then a 2-stage process as the fork cap and fork cartridge are removed together from the fork tube, and then the fork cap is removed from the fork cartridge. These features are shown in FIGS. 1-3.
Modern suspension is becoming increasingly complicated both in function and servicing. The newer style forks have separated oil chambers for rebound and compression. In order to service the fork, either for modification (tuning) or for simply changing the oil, the entire fork must be disassembled. Typically, the fork will be held in a specialized vice during this process. Once the fork cap is unthreaded and removed the user must now unscrew the compression cartridge from the fork cap. Much care must be taken during this process as the parts are delicate and often are anodized. Scratching the anodizing is undesirable to the owners. Once the cap is removed, the fork cap socket (outer) is placed in a vice to prevent it from moving and the fork cartridge rotated to unscrew it from the fork cap.
FIG. 1 shows a front view of a motorcycle 1 showing the location of the fork 2 including the forks tube assemblies 3 and the wheel 4. Each fork assembly 3 includes a fork inner leg 5 and a fork outer leg 6, which are filled with oil 7. The inner leg 5 slides within the outer leg 6, and there is an oil seal 8 at the telescoping juncture of the two. The fork cartridge 22 extends within the fork tubes assemblies 3 and provides additional shock reduction. A fork cap 24 attaches to the fork cartridge 22 and then attaches in turn to the fork outer leg 6.
FIG. 2 shows a detail view of the end 20 of a fork 2 with a fork cartridge 22 inserted, and held in position by a fork cap 24 to make what will be termed a fork end assembly 26. FIG. 3 shows an exploded view of the fork end assembly 26. It will be understood that there is typically some sort of sealing ring included with the fork cap 24, but this is not shown here for sake of simplicity. The inner bore 30 of the fork end 20 is generally threaded to make a threaded inner bore 32, and the outer surface 34 of the fork cap 24 is configured with mating threads to make a threaded outer surface 36. The inner bore 38 of the fork cap 24 is also configured as a cap threaded inner bore 40, and the outer surface 42 of the fork cartridge 22 is configured with mating threads to make a cartridge threaded outer surface 44.
Thus, the fork cartridge 22 screws into the fork cap 24 and the fork cartridge 22 together with the fork cap 24, which will be termed the fork cartridge assembly 46, is then screwed into the fork end 20 to make the fork end assembly 26.
To aid in turning the fork cartridge assembly 46 with respect to the fork end 20, or the fork cap 24 with respect to the fork cartridge 22, the fork cap 24 is provided with an octagonal outline 48, which can be engaged with a wrench. The fork cartridge 22 is also configured with a flanged top 50, with a ridge 52, which can be gripped to turn the fork cartridge 22 with respect to the fork cap 24.
The removal of the fork cartridge 22 is thus performed in two stages. First, the fork cartridge assembly 46, which includes the fork cartridge 22 and fork cap 24, is unscrewed from the fork end assembly 26, as the fork 2 is held in a vise, or otherwise restrained from turning. Second, the fork cartridge 22 is unscrewed from the fork cap 24, as the fork cap 24 is held in a vise. Thus, for the first stage, a wrench of appropriate size and configuration is used to grip the octagonal outline 48 of the fork cap 24. Then, in the second stage, a tool must be found to grip the ridge 52 of the fork cartridge 22. Motorcycle repair shops commonly use sets of socket wrenches with a ratchet handle for mechanical operations, but the ridge on the top of the fork cartridge generally requires a different tool, which may require some effort to locate, thus wasting time. It would be much more efficient if a single tool adapted for both operations could be used that allow easy manipulating of both stages of removal.
There is an existing tool on the market that is designed for removing a fork cartridge, and is generally configured as a one piece long box wrench made from 2 mm thick aluminum or steel that fits the fork cap. This existing tool also has a rectangular slot in the handle portion that is designed to fit over the fork cartridge ridge 52. However, in order to use this tool to remove the fork cartridge 22 from the fork cap 24, it requires either the use of two of these tools, one to hold the fork cap 24 by the hex outer shape 48 and another to grip the ridge 52 on the fork cartridge or, using only one of these tools, by clamping the fork cap cartridge hex 48 in a vise and then using the rectangular slot feature on the existing tool to grip and turn the ridge 52 on the fork cartridge 22.
However, there are several problems with using the existing tool as described above: 1) the ridge 52 on the fork cartridge rises only about 2 mm above the height of the top of the fork cap when assembled and thus provides a very limited purchase for attachment of the existing tool to the ridge 52. 2) when used with the fork cap octagonal outline 48 clamped in a vise to hold it, the octagonal outline 48 part of the fork cap 24 must be very carefully positioned so that the top of the fork cap is flush with the top of the vice and allows the slot on the existing tool to get maximum possible purchase on the ridge 52 of the fork cartridge 22. This is difficult and time consuming to do, and often ends in frustration and damage to the fork cap and or the fork cartridge.
The manufacturer of the fork recommends using a 36 mm socket to grip and turn the ridge 52 on the fork cartridge while the fork cap octagonal outline 48 is clamped in a vice. This method allows more leeway in clamping the fork cap octagonal outline 48 because the top of the fork cap 24 can be below the top of the vice and the socket (if long enough) can still get full purchase along almost the entire height of the fork cartridge ridge 52. However, the problem with this method is that the elongated hexagonal shape of the ridge 52 only allows the socket wrench to engage two of the points in the socket, with very limited contact area and does not provide a very secure grip on the fork cartridge ridge 52 (a hex socket normally engages six flats on a hex head to provide many more times the contact area).
If the tool slips as torque is applied, this could easily result in damage to the fork cartridge, which once damaged cannot be repaired. The manufacturer does not offer replacement fork caps or cartridges separately and requires that the entire assembly be purchased together at a cost of several hundred dollars.
Thus, there is a need for a fork cartridge driver which provides a single tool which can be adapted to both stages of the removal process and which is usable to engage both the fork cartridge and the fork cap.
There is further a need for a tool that provides a much better and secure grip on the parts that are being disassembled and reassembled and thereby greatly reduces the likelihood of damage to those parts that are very expensive to replace.